Stoats make a splash

Sep 16, 2013
Stoats make a splash
Ten stoats from Lincoln University, were put into a water-filled flume with a continuous current flowing through it, to watch how far they could swim.

Stoats are generally considered capable of swimming up to about 1.5km, but the discovery of a stoat on Rangitoto Island (3 km offshore) in 2010, and another on Kapiti (5 km offshore) in 2011 suggested they may be able to get their little legs paddling for much greater distances.

Experiment on the distance a stoat can swim

University of Waikato Associate Professor Carolyn (Kim) King and a team from the Faculty of Science and Engineering decided to find out just how far.

So she bought ten stoats from Lincoln University, flew them to Hamilton, allowed them to jump into a water-filled flume with a continuous current flowing through it, and watched them go.

One female – clearly the Lauren Boyle of the stoat world – covered 1.8km in nearly two hours non-stop swimming, while three others swam strongly for more than an hour and another four chalked up between 20 and 40 minutes paddling.


Only one struggled with the swimming, having the stoat equivalent of a panic attack after about ten minutes in the water while the other was suffering from a , so was retrieved after a few minutes. After their swimming efforts, the stoats were taken for blood tests to measure their blood glucose. Those which swam longest had consistently lowered , consistent with induced by .

While the results were not conclusive, the study did show that stoats were capable of swimming much greater distances than previously thought, a fact which has implications for offshore island wildlife sanctuaries once believed to be at little or no risk of invasion by stoats.

About 250 of New Zealand's are reserves, and many of them shelter various threatened and endangered .

Issue of reinvasion on offshore reserves

More than 100 islands have been cleared of invasive mammals, but the problem of reinvasions from the mainland remains a serious issue.

Maud Island in the Marlborough Sounds is only 900m from the mainland and has been reinvaded by pregnant female stoats three times since 1982, while stoats long ago populated Chalky Island in Fiordland, which is 2.5km from the mainland but accessible via three intermediate islands.

The generally accepted risk-zones around islands 1.5km offshore "have been seriously underestimated," Associate Professor King says.

While her tests showed that at least one captive stoat could swim 1.8km in nearly two hours, "a fit and active wild stoat free to choose its own time, motivation and swimming speed might swim much further, especially given the added buoyancy of salt water".

One stoat in the tests also showed an ability to rest while floating, which could extend their range even further, Associate Professor King says. Favourable currents, floating logs or stepping stone islands would also increase their range.

Females, though smaller than males and invariably pregnant, showed no signs of being inferior swimmers, and posed a "special risk" to islands they reached through their ability to start a new population through sibling breeding – as happened on Kapiti.

The team concluded the tests, plus independent modelling, show islands less than 3.5km offshore should still be considered at risk of invasion by stoats and the common assumption that permanently maintained traplines on such islands were not necessary was "a false economy".

Associate Professor King's research is due to be published in the academic journal Biological Invasions. She will also deliver a talk about her study at the Ecological Society conference in Auckland in November.

Explore further: On genetic treasure island, voles show DNA antiquity

add to favorites email to friend print save as pdf

Related Stories

On genetic treasure island, voles show DNA antiquity

Sep 06, 2013

( —With its snubby, blunt nose, small, furry ears and short tail, the Orkney Islands vole may not seem significant, but it harbors genetic secrets that can help shed light on novel evolutionary ...

Rare parakeets to populate gulf islands

Jan 29, 2008

An ambitious plan to translocate 100 kakariki (red-crowned parakeets) from Little Barrier Island to two other Hauraki Gulf islands as well as a mainland site means more people will be able to see the rare ...

New Zealand bird outwits alien predators

Jun 04, 2008

New research published in this week's PLoS ONE, led by Dr Melanie Massaro and Dr Jim Briskie at the University of Canterbury, which found that the New Zealand bellbird is capable of changing its nesting behaviour to protect ...

Recommended for you

Male monkey filmed caring for dying mate (w/ Video)

Apr 18, 2014

( —The incident was captured by Dr Bruna Bezerra and colleagues in the Atlantic Forest in the Northeast of Brazil.  Dr Bezerra is a Research Associate at the University of Bristol and a Professor ...

Orchid named after UC Riverside researcher

Apr 17, 2014

One day about eight years ago, Katia Silvera, a postdoctoral scholar at the University of California, Riverside, and her father were on a field trip in a mountainous area in central Panama when they stumbled ...

In sex-reversed cave insects, females have the penises

Apr 17, 2014

Researchers reporting in the Cell Press journal Current Biology on April 17 have discovered little-known cave insects with rather novel sex lives. The Brazilian insects, which represent four distinct but re ...

Fear of the cuckoo mafia

Apr 17, 2014

If a restaurant owner fails to pay the protection money demanded of him, he can expect his premises to be trashed. Warnings like these are seldom required, however, as fear of the consequences is enough to ...

User comments : 0

More news stories

Researchers successfully clone adult human stem cells

( —An international team of researchers, led by Robert Lanza, of Advanced Cell Technology, has announced that they have performed the first successful cloning of adult human skin cells into stem ...

NASA's space station Robonaut finally getting legs

Robonaut, the first out-of-this-world humanoid, is finally getting its space legs. For three years, Robonaut has had to manage from the waist up. This new pair of legs means the experimental robot—now stuck ...

Ex-Apple chief plans mobile phone for India

Former Apple chief executive John Sculley, whose marketing skills helped bring the personal computer to desktops worldwide, says he plans to launch a mobile phone in India to exploit its still largely untapped ...

Filipino tests negative for Middle East virus

A Filipino nurse who tested positive for the Middle East virus has been found free of infection in a subsequent examination after he returned home, Philippine health officials said Saturday.

Egypt archaeologists find ancient writer's tomb

Egypt's minister of antiquities says a team of Spanish archaeologists has discovered two tombs in the southern part of the country, one of them belonging to a writer and containing a trove of artifacts including reed pens ...